In vivo imaging of antioxidant response element activity during liver regeneration after partial hepatectomy

Transcriptomic Characterization of Key Factors and Signaling Pathways for the Regeneration of Partially Hepatectomized Liver in Zebrafish

Liver regeneration induced by partial hepatectomy (PHx) has attracted intensive research interests due to the great significance for liver resection and transplantation. The zebrafish (Danio rerio) is an excellent model to study liver regeneration. In the fish subjected to PHx (the tip of the ventral lobe was resected), the lost liver mass could be fully regenerated in seven days. However, the regulatory mechanisms underlying the liver regeneration remain largely unknown. In this study, gene expression profiles during the regeneration of PHx-treated liver were explored by RNA sequencing (RNA-seq). The genes responsive to the injury of PHx treatment were identified and classified into different clusters based on the expression profiles. Representative gene ontology (GO) enrichments for the early responsive genes included hormone activity, ribosome biogenesis and rRNA processing, etc., while the late responsive genes were enriched in biological processes such as glutathione metabolic process, antioxidant activity and cellular detoxification. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichments were also identified for the differentially expressed genes (DEGs) between the time-series samples and the sham controls. The proteasome was overrepresented by the up-regulated genes at all of the sampling time points. Inhibiting proteasome activity by the application of MG132 to the fish enhanced the expression of Pcna (proliferating cell nuclear antigen), an indicator of hepatocyte proliferation after PHx. Our data provide novel insights into the molecular mechanisms underlying the regeneration of PHx-treated liver.

Targeting NRF2 to promote epithelial repair

The transcription factor NRF2 is well known as a master regulator of the cellular stress response. As such, activation of NRF2 has gained widespread attention for its potential to prevent tissue injury, but also as a possible therapeutic approach to promote repair processes. While NRF2 activation affects most or even all cell types, its effect on epithelial cells during repair processes has been particularly well studied. In response to tissue injury, these cells proliferate, migrate and/or spread to effectively repair the damage. In this review, we discuss how NRF2 governs repair of epithelial tissues, and we highlight the increasing number of NRF2 targets with diverse roles in regulating epithelial repair.

Cerium oxide nanoparticles improve liver regeneration after acetaminophen-induced liver injury and partial hepatectomy in rats

Background and aims

Cerium oxide nanoparticles are effective scavengers of reactive oxygen species and have been proposed as a treatment for oxidative stress-related diseases. Consequently, we aimed to investigate the effect of these nanoparticles on hepatic regeneration after liver injury by partial hepatectomy and acetaminophen overdose.

Methods

All the in vitro experiments were performed in HepG2 cells. For the acetaminophen and partial hepatectomy experimental models, male Wistar rats were divided into three groups: (1) nanoparticles group, which received 0.1 mg/kg cerium nanoparticles i.v. twice a week for 2 weeks before 1 g/kg acetaminophen treatment, (2) N-acetyl-cysteine group, which received 300 mg/kg of N-acetyl-cysteine i.p. 1 h after APAP treatment and (3) partial hepatectomy group, which received the same nanoparticles treatment before partial hepatectomy. Each group was matched with vehicle-controlled rats.

Results

In the partial hepatectomy model, rats treated with cerium oxide nanoparticles showed a significant increase in liver regeneration, compared with control rats. In the acetaminophen experimental model, nanoparticles and N-acetyl-cysteine treatments decreased early liver damage in hepatic tissue. However, only the effect of cerium oxide nanoparticles was associated with a significant increment in hepatocellular proliferation. This treatment also reduced stress markers and increased cell cycle progression in hepatocytes and the activation of the transcription factor NF-κB in vitro and in vivo.

Conclusions

Our results demonstrate that the nanomaterial cerium oxide, besides their known antioxidant capacities, can enhance hepatocellular proliferation in experimental models of liver regeneration and drug-induced hepatotoxicity.

Effect of dioscin on promoting liver regeneration via activating Notch1/Jagged1 signal pathway

BACKGROUND

Development of novel candidates to promote liver regeneration is critical important after partial hepatectomy (PH). Dioscin, a natural product, shows potent effect on liver protection in our previous works.

PURPOSE

This work aimed to investigate the effect and underlying mechanisms of dioscin on liver regeneration.

METHODS

The promoting proliferation effects of dioscin on mouse hepatocytem AML12 cells, rat primary hepatocytes, rats and mice after 70% PH were evaluated.

RESULTS

Dioscin significantly promoted proliferation of rat primary hepatocytes and AML12 cells through MTT, BrdU and PCNA staining assays. Meanwhile, dioscin rapidly recovered the liver to body weight ratios, declined ALT and AST levels, and relieved hepatocytes necrosis compared with 70% PH operation groups in rats and mice. Mechanistic test showed that dioscin significantly increased Notch1 and Jagged1 levels, and accelerated γ-secretase activity by up-regulating PS1 expression, leading to nuclear translocation of Notch1 intracellular domain (NICD1). Subsequently, the significant activation of Notch-dependent target genes (Hey1, Hes1, EGFR, VEGF), and cell-cycle regulatory proteins (CyclinD1, CyclinE1, CDK4 and CDK2) were all recognized. In addition, these results were further confirmed by Notch1 siRNA silencing and inhibition of γ-secretase by DAPT (a well-characterized γ-secretase inhibitor) in vitro.

CONCLUSIONS

Dioscin, as a novel efficient γ-secretase activator, NICD1 nucleus translocation promoter and cell cycle regulator, markedly activated Notch1/Jagged1 pathway to promote hepato-proliferation. Our findings provide novel insights into dioscin as a natural product with facilitating liver regeneration after PH.

Expression of VEGFR-2 during Liver Regeneration after Partial Hepatectomy in a Bioluminescence Mouse Model

BACKGROUND

Liver regeneration requires the formation of new blood vessels. Endothelial cell proliferation is stimulated by vascular endothelial growth factor (VEGF) and its receptor tyrosine kinase VEGFR-2. The aim of this study was to investigate VEGFR-2 expression in vivo during liver regeneration after partial hepatectomy (PHx).

METHODS

Transgenic VEGFR-2-luc mice were used in which the luciferase reporter gene was under control of the VEGFR-2 promoter. Following 2/3 PHx, the mice underwent in vivo bioluminescence imaging until the 14th postoperative day. Additionally, liver tissue was analyzed by immunohistochemistry, in vitro luminescence assays, and quantitative RT-PCR.

RESULTS

In vivo bioluminescence imaging showed a significant increase in VEGFR-2 promoter activity after PHx. Maximum signal was recorded on the 3rd day; 8 days postoperatively the signal intensity decreased significantly. On the 14th day, bioluminescence signal reached almost baseline levels. Immunohistochemistry, quantitative RT-PCR, and in vitro luminescence confirmed a significant increase on the 3rd day following resection. The mRNA expression of VEGFR-2 was significantly higher on day 3 than preoperatively as well as on day 8.

CONCLUSION

In vivo bioluminescence imaging with transgenic VEGFR-2-luc mice is feasible and provides a convenient model for noninvasively studying VEGFR-2 expression during liver regeneration. This may facilitate further experiments with modulation of angiogenesis by different substances.